The present invention is directed to a measuring instrument for an optical medium, which instrument utilizes two optical transmitters and two optical receivers, with one optical receiver and transmitter being coupled to the optical medium on one side and the other receiver and transmitter being coupled to the medium on the opposite side.
Both allowed U.S. patent application Ser. No. 07/394,114, filed Aug. 15, 1989, which issued on Jan. 7, 1992 as U.S. Pat. No. 5,078,489, whose disclosure is incorporated herein by reference thereto, and which claims priority from German Application 38 28 604 as well as U.S. Pat. No. 4,652,123, whose disclosure is incorporated herein by reference thereto, disclose a measuring device which utilizes an optical transmitter and optical receiver means on one side of an optical medium to be measured and a transmitter and receiver means on the opposite side. In short, the measuring principle consists thereof that on one side of the optical medium, which may be in the shape of a light waveguide splice, a coupler or other passive optical component, an optical transmitter is connected, which couples its measuring signal in a light waveguide leading to the optical medium. From this first measuring transmitter, two measuring signals are obtained by means of two measuring receiver means, namely once before the optical medium and once after the optical medium. In the same way, an optical transmitter is then coupled to the other side of the optical medium and, again, a measuring of the reception signal is performed by means of the two receiver means, one located before the optical medium and the other following the optical medium. All in all, this operating mode, thus, requires two optical transmitters and two optical receivers. From the obtained test signal, it is possible to determine in exact fashion the attenuation of the optical medium in the manner described in the above-mentioned allowed U.S. application.
In many cases it is necessary to perform the measurement at the operating location, for example when splicing a light waveguide cable. This requires that the measuring instrument, as such, is fashioned to be transportable and that the requirement exists that the measuring operation can be performed by an operator as easily and as quickly as possible, whereby measuring results are to be obtained that can be reproduced as accurately as possible.